The present invention relates to a method for protectively fixing a joint of electrical wires, and more particularly to a method for forming a cover layer over a joint of electrical wires.
Conventionally, wires having a layer of insulation made of a material such as vinyl resin have been joined by the following process. First, the insulation is stripped back by a predetermined length and the wires assembled to thereby expose the conductor. The conductors from the wires to be joined are then twisted together or arranged side by side. A conductive sleeve is next fitted over the conductors under pressure, or the conductors are soldered together, to form a joint. The joint thus formed is covered with an insulating tape or the like for insulation and protection.
The above-described conventional technique, however, is disadvantageous in that it is often difficult to adequately electrically insulate the joint, the insulating effect provided by the tape is not uniform, and the tape has only a low mechanical strength.
To overcome these drawbacks, it has been proposed to form an insulating layer over a wire joint by resin molding. In such a method, the joint is set together with insulating sheaths in a metal mold and, for instance, vinyl chloride resin is injected into the mold to thereby seal the joint with an insulating resin layer. The insulating sheaths are covered tightly with the insulating resin layer.
However, the proposed method is still disadvantageous in that, even if the insulating sheath and the insulating resin layer are made of the same material, for example, soft vinyl chloride resin, they often are not fused together in the mold due, for instance, to temperature differences. Hence, because the insulating sheath and the insulating resin layer do not completely adhere to one another, moisture can seep into the connection area of the electrical wires. Also, this conventional method is disadvantageous in that the number of process steps is large and the molding operation rather difficult to perform. Moreover, the method often results in the production of an insulating resin layer which was not uniform in thickness.
To eliminate the adhesion problem, it has been proposed to apply an adhesive to the surfaces of the insulating sheaths before the joint of the wires is set in the mold to thus improve the adhesion between the insulating sheath and the insulating resin layer. While the adhesion may be improved, extra steps are of course required. Also, the other problems mentioned above remain.